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M2 | Microbiolgy > Bacterial Dysentery > Flashcards

Bacterial Dysentery Flashcards

1
Q

How Enterohemorrhagic Escherichia coli is transmitted ?

A
  1. Ingestion of undercooked meat 🥩
  2. Direct contact with animals (Main reservoir is cattle)
  3. Ingestion of undercooked hamburger at fast-food restaurants ——-> Associated with outbreaks of bloody diarrhea
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2
Q

Pathogenesis of Enterohemorrhagic E.coli bloody diarrhea

A
  • Dysentery-like syndrome characterized by bloody diarrhea

* abdominal cramping & fever (similar to Shigella) —-> by producing “Shiga toxin” or “verotoxin” ( endotoxin )

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3
Q

What is the mechanism of shiga toxin ?

A

acts by removing adenine from large (28S) ribosomal RNA, thereby stopping protein synthesis

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4
Q

Pathogenesis of HUS in EE.coli

A

HUS ——> Hemolytic–uremic syndrome

  • complication consists of hemolytic anemia, thrombocytopenia & acute renal failure
  • Endothelium of small blood vessels & kidney epithelium has Shiga toxin receptors
  1. Death of kidney epithelial cells ——> renal failure
  2. Death of small blood vessels endothelial cells—> hemolytic anemia (red cells passing through damaged area become distorted (schistocytes) & lyse
  3. Thrombocytopenia (platelets adhere to damaged endothelium)
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5
Q

Enteroinvasive Escherichia coli (EIEC) invades the epithelium of which organ ?

A

Large intestine

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6
Q

EIEC causes bloody diarrhea (dysentery) accompanied by ___________ in stool.

A

inflammatory cells (neutrophils)

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7
Q

How to diagnose Enterohemorrhagic E.coli ?

A

cultured on Sorbitol MacConkey’s agar does not ferment sorbitol (distinguishes it from other strains of E. coli)

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8
Q

Important properties of salmonella

A
  • Gram-negative rods

* do not ferment lactose & produce H2S

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9
Q

State the antigens of salmonella

A
  1. “O” antigens: Outer polysaccharides of cell wall

2- ”H “ antigens: Flagellar antigens

3- “Vi” antigens: Capsular polysaccharides

  • Antiphagocytic (important virulence factor for S. typhi)
  • Serotyping of S. typhi in clinical laboratory
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10
Q

Mode of Transmission in salmonella

A

Ingestion of food & water contaminated by human & animal wastes

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11
Q

How human’s are a source of salmonella infection?

A
  1. Persons excrete organism during or shortly after attack of enterocolitis
  2. Chronic carriers: excrete organism for years
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12
Q

How animals are a source of salmonella infection?

A
  1. Poultry, eggs & undercooked meat

2. Dogs & other pets

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13
Q

Which type of salmonella is transmitted only in humans ?

A

S. typhi ( typhoid fever )

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14
Q

How Enterocolitis occur ?

A
  1. Invasion of epithelial & subepithelial tissue of small & large intestines inflammation & diarrhea
  2. Enterocolitis with nausea & vomiting then abdominal pain & diarrhea
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15
Q

What is the infectous dose of salmonella?

A

at least 100,000 organisms

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16
Q

What lowers the salmonella’s infectous dose?

A

Gastrectomy or use of antacids

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17
Q

What happens to HIV-infected individuals with salmonella infection?

A

They have low CD4 count ———> Salmonella infections

  • severe diarrhea
  • serious metastatic infections
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18
Q

What is the incubation period of Enterocolitis in salmonella?

A

12 to 48 hours

19
Q

Pathogenesis of Typhoid fever (S. typhi)& Enteric fever (S. paratyphi A, B & C)

A
  1. Organisms enter & multiply in mononuclear phagocytes of Peyer’s patches of small intestine ——-> phagocytes of liver, gallbladder & spleen ——> bacteremia & fever caused by endotoxin
  2. Salmonella invades gallbladder ———> carrier state & excretion of bacteria in feces for long periods
    * Salmonella survive within phagosomes in phagocytic cells
20
Q

What is the clinical findings of Typhoid fever (S. typhi)& Enteric fever (S. paratyphi A, B & C)?

A
  1. Fever & constipation rather than vomiting & diarrhea
  2. Diarrhea occur early but disappears & fever & bacteremia occur
  3. After 1st week ——> high fever, delirium, tender abdomen & enlarged spleen occur
  4. Rose spots (rose-colored macules on abdomen)
  5. Leukopenia & anemia
  6. Abnormal liver function ——-> hepatic involvement
  7. Severe complications : intestinal hemorrhage or perforation
21
Q

Pathogenesis of Septicemia (S. choleraesuis)

A
  1. Bacteremia ——-> osteomyelitis (child with sickle cell anemia) , pneumonia & meningitis
  2. Infarcts & aneurysms are most sites of metastatic abscesses
  3. Vascular graft infections
    * Fever but little or no enterocolitis
22
Q

Laboratory diagnosis of Enterocolitis

A

Salmonella is isolated from stool sample

23
Q

Laboratory diagnosis of enteric fever

A
  1. Blood culture : first 2 weeks of illness
  2. Bone marrow cultures : positive
  3. Stool cultures positive in chronic carriers (Salmonella is secreted in

bile into intestinal tract)

  1. Slide agglutination test:
    * Salmonella serogroup based on its O antigen
    * Serotyping of O, H & Vi antigens for epidemiology
  2. Serologically (Widal test):
    * detecting rise in antibody titer in patient’s serum in enteric fever
    * sepsis when organism is difficult to recover
24
Q

What does salmonella form in MacConkey’s agar/ EMB agar ?

A

non-lactose-fermenting (colorless) colonies

25
How to diagnose salmonella in TSI agar ?
alkaline slant & acid butt with both gas & H2S
26
S. typhi : does not form____ & produces only small amount of _____
Doesn’t form gas | Only small amount of H2S
27
Important properties of Shigellae
* non–lactose-fermenting * gram-negative rods * produce no gas from fermentation of glucose * do not produce H2S * non motile * All shigellae have O antigens (polysaccharide) in their cell walls
28
What is the mode of transmission in shigellae ?
* Shigellosis is only human disease * Fecal–oral route * No prolonged carrier state
29
What is the infectious dose of shigellae ?
Very low infectious dose; ingestion of 100 organisms cause disease
30
Clinical findings of shigellae
1. Bloody diarrhea (Bacillary dysentery) : * by invasion of colonic microfold cells (critical factor) 2. Some strains produce enterotoxin (Shiga toxin) 3. Local inflammation accompanied by ulceration 4. Fever & abdominal cramps followed by diarrhea with blood & mucus
31
Incubation period of shigellae
1 to 4 days
32
How shigellae is identified in MacConkey’s agar ?
non–lactose-fermenting (colorless) colonies
33
How shigella appear in TSI agar ?
alkaline slant & acid butt, with no gas & no H2S
34
Important properties of Campylobacter jejuni
* Curved, comma- or S shaped gram-negative rods | * Microaerophilic, growing best in 5% oxygen at 42°C
35
Transmission of C.jejuni
* Fecal–oral
36
What are the human sources causing C.jejuni infection?
1. Domestic animals: cattle, chickens & dogs 2. Foods: chicken, meat, unpasteurized milk & water contaminated with animal feces 3. Human-to-human transmission occurs
37
Clinical findings of C.jejuni
1. Inflammation of intestinal mucosa 2. Enterocolitis begins as * watery, foul-smelling diarrhea * followed by bloody stools with fever & severe abdominal pain 3. Bacteremia: * in neonates or debilitated adults
38
C.jejuni is associated with which syndrome and explain its pathogenesis?
Guillain-Barré syndrome (acute neuromuscular paralysis) ——> It is an autoimmune disease due to formation of antibodies against C. jejuni that cross-react with antigens on neurons
39
Laboratory diagnosis of C.jejuni
1. Diarrheal stool specimen: * cultured on blood agar plate containing antibiotics that inhibit other fecal flora 2. Incubated at 42°C in microaerophilic atmosphere containing 5% oxygen & 10% carbon dioxide 3. Failure to grow at 25°C 4. Oxidase positivity 5. Sensitivity to nalidixic acid 6. Blood culture (bacteremia): * growth of comma- or S-shaped, motile, gram-negative rods
40
Important properties & transmission of Yersinia enterocolitica
* Gram-negative rods * Transmission: 1. fecal contamination of food; raw pork (most commonly) 2. unpasteurized milk products 3. unfiltered water
41
Pathogenesis of Yersinia enterocolitica
* Enterocolitis (similar to Shigella & Salmonella) * Mesenteric adenitis (mimic appendicitis): inflammation of the lymph nodes in the abdomen * Rarely, bacteremia or abscesses of liver or spleen, in persons with underlying disease
42
How Y. enterocolitica appear in stool culture?
lactose negative colony on MacConkey’s agar
43
What is the Cold enrichment technique ?
stool sample incubation at 4°C for 1 week increases recovery of organism
44
At which degree the Y. enterocolitica grows ?
Grows better at 25°C than at 37°C

M2 | Microbiolgy (17 decks)

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